1. Field of the Invention
This invention relates to a belt-type continuously variable transmission apparatus, and more particularly to a V-belt continuously variable transmission apparatus wherein the transmission gear ratio can be controlled by an electric actuator.
2. Description of Background Art
A V-belt continuously variable transmission apparatus is known wherein a V-belt extends between and around a driving pulley connected to a prime mover such as an engine and a driven pulley connected to a load and the wrapping diameters of the V-belt on the driving pulley and the driven pulley are varied continuously to control the transmission gear ratio. In order to vary the wrapping diameters of the V-belt, from between a fixed pulley part and a movable pulley part which form each of the driving pulley and the driven pulley, the movable pulley part is displaced in an axial direction of a support shaft therefor to vary the distance between the pulley parts to vary the wrapping diameter.
For example, a continuously variable transmission apparatus wherein a movable pulley part is driven by a motor is disclosed in Japanese Patent Laid-Open No. Hei 5-44827. In the continuously variable transmission apparatus, the movable pulley part of the driving pulley is coupled to a slider through a bearing and the slider is connected to a motor through a gear.
The control of the transmission gear ratio is performed detecting an operation condition of the engine from the speed of rotation of the engine, the throttle opening and so forth. Whether the transmission gear ratio has an appropriate value is detected as the position of the movable pulley part, and the motor is feedback controlled based on the detected position of the movable pulley part.
The continuously variable transmission apparatus mentioned above includes: a power transmission case formed integrally with a crankcase of an engine and forming a partition wall from a crankcase, a power transmission case cover for covering the power transmission case, and an outer cover for covering the power transmission case cover. Since the outer cover closes up air circulating holes for cooling and so forth and is formed attaching importance to the appearance design, the transmission apparatus is protected substantially by the power transmission case and the power transmission case cover. Accordingly, a transmission apparatus wherein a slider is connected to a motor through a gear system and is moved by the motor to control the transmission gear ratio is configured such that they are covered with a power transmission case cover.
However, in order to form the power transmission case cover in such a manner as to cover the gear system and the motor, a complicated configuration must be formed integrally. To this end, the mold for manufacture is obliged to be complicated, and also assembly to the power transmission case is not easy.